Bell jar model lung

This simple model can be used to demonstrate the basic principles of
breathing. The model should be assembled as in the diagram. A swimming
cap makes a suitable diaphragm. The cap can be attached to the bottom
of the bell jar, and the balloons can be attached to the Y shaped tube,
with elastic bands or plastic coated wire.
How the Model Works
The cavity inside the bell jar is airtight. As the diaphragm is pulled down,
the volume of the cavity increases. This causes the pressure to fall. Air
rushes in to equalise the pressure causing the balloons to inflate.